1. Field of the Invention
The invention relates to a method for the manufacture of a shaft seal, as well as to the resulting shaft seal.
2. Description of the Prior Developments
In a known seal of this type (EP-A-139,503) firstly the shaft seal ring is shaped onto the radial flange of a cross-sectionally L-shaped sheet metal ring. For connection to a gasket receptacle, the outer, axially parallel portion of the ring is inserted in the cavity of an injection mould, so that in the case of the finished seal the outer portion of the sheet metal ring is received in a recess, in the form of an inner groove, of the gasket receptacle in the form of a plastic moulding and is fastened to the receptacle on both sides by elastomer material, which is also used for the static gasket and is linked therewith. The thus formed gasket module comprising the gasket receptacle with the shaft seal ring and the static gasket leads to a prefabricated, interchangeable unit. The described fastening by the axially parallel portion of the L-shaped sheet metal ring requires the shaping of the plastic gasket receptacle on the sheet metal ring, either before or after shaping the shaft seal ring on the inner portion of the sheet metal ring. The elastomer material injected on either side of the axially parallel portion ensures an elastic fastening. As a result of this design type the necessary limited radial tolerances for obtaining the coaxial nature of the sealing lip to the shaft are not always respected. Problems are also caused by the settling or creep of the plastic moulding under screw force, which can lead to leaks between the crankcase and the seal.
For the main use of the invention of the driven side crankshaft seal in motor vehicles, in which the crankshaft, the end wall of the crankcase and the crankcase wall perpendicular thereto are to be sealed with respect to the oil pan or sump, a seal with a light metal pressure die casting as the gasket receptacle has proven completely satisfactory. For the assembly of such a seal all the parts, namely the radial shaft seal ring, the pressure die casting, a flat gasket serving as a static gasket over the end wall of the crankcase, etc. are individually made available, which requires numerous working steps during assembly. This multipart solution leads to many error possibilities and in particular the possibility of damaging the individual components of the shaft seal. In this connection tests carried out by the applicant have revealed that shaft seals often have to be disposed of as waste due to damage in the sealing edge area of the shaft seal ring.
The object of the invention is to provide a method for the manufacture of a seal, in which the dynamic shaft seal ring and also the static gasket housed in a gasket receptacle are made available in the form of a prefabricated unit. Use is largely made of proven components and in particular the light metal pressure die casting for the reception of the gaskets. The aim is to render reusable the relatively expensive pressure die castings even in the case of a fault, particularly with respect to the shaft seal ring. Identical pressure die castings are to be rendered usable for different gasket modules for initial installation and for use as spares in after-sales service.
In a known concept, in which a shaft seal ring and a static gasket are shaped onto a gasket receptacle for forming a shaft seal with a single moulding tool (DE-C 3,634,735), in which the gasket receptacle is drawn from a metal sheet, the following difficulties are encountered which are prejudicial to prefabrication.
As the pressure die castings are not machined and are manufactured with the relatively large tolerances of the pressure die casting process, the moulding tool must be designed in such a way that there is a plastic deformation of the die casting carrier on the impression edges. In a second production attempt in the same moulding tool, the latter no longer brings about a satisfactory impression on the recovered carrier and overfilling takes place.
The requirement of shaping onto the die casting carrier the dynamic and the static gasket in the same moulding tool, makes such tools very expensive to manufacture and maintain, because the very much higher requirements made on the quality of the dynamic gasket, i.e. the shaft seal ring, define the costs.
The volume of the metal parts to be inserted in the tools has a disadvantageous influence on the manufacturing conditions and in particular on the time up to uniform heating to the moulding tool temperature.
In the known concept the higher technical requirements regarding the manufacture of the dynamic sealing edge determine the requirements on the die casting machine and the cycle time. Thus, the much more easily manufactured static gasket is necessarily produced with excessive expenditure.
The manufacture of the gasket according to the known concept requires high capital expenditure with respect to new and large die casting machines with a maximum precision high closing force, which must be suitable for the manufacture of radial shaft seal rings, whereas existing smaller die casting machines must be shut down for such radial shaft seal rings, because these products are substituted by the new gaskets.
A gasket system for a dynamic shaft seal not only comprises the sealing element, but also the antirotation face on the rotating surface. If such a seal fails due to leaks and has to be replaced, then nowadays for the replacement of radial shaft seal rings during the second installation the seal is pressed roughly 1 mm deeper into the casing bore. As a result comparable conditions to the initial installation are obtained, i.e. a new sealing lip on the new antirotation face of the shaft. However, this is only possible if for the initial installation and repair two different parts are manufactured, which require two different, relatively expensive pressue die cast parts and two different die casting tools.
The operating conditions generally require for the dynamic gasket a much more expensive elastomeric material (generally based on fluorine elastomer FPM) than for the static gasket. Particularly in the case of large gasket modules clear cost advantages would result from using different elastomeric materials for the static and the dynamic gaskets. However, this is not possible with the known concept.